1. Field of the Invention
The present invention relates to a vehicle controller, and more particularly to a vehicle controller for controlling an actuator, such as a motor, in a vehicle control system that enables driving, steering and braking of a vehicle to be performed under electronic control.
2. Description of the Related Art
Recently, aiming at improving comfortableness and safety in running of an automobile, a vehicle control system (called an X-by-Wire system) has been more actively developed which serves to reflect driver's operations, such as accelerating, steering and braking operations, on vehicle mechanisms for generating driving, steering and braking forces, respectively, through electronic control without employing mechanical linkages. Such a system is required to have high reliability so that the vehicle driving, steering and braking functions are in no way failed.
To increase reliability of the overall system, a controller constituting the system is also required to realize high reliability. Various types of failsafe designs have hitherto been proposed for a controller that controls a motor. Many of the failsafe designs employ a redundant arrangement in which the operation of a first microcomputer (main microcomputer) is monitored by a second microcomputer (monitoring microcomputer).
There is known, for instance, an exercise computation technique in which the monitoring microcomputer sets an exercise (example problem) to the main microcomputer. The main microcomputer computes an answer of the exercise and sends it to the monitoring microcomputer. Then, the monitoring microcomputer compares the answer sent from the main microcomputer with an answer stored therein beforehand. It is thereby checked whether the operation of the main microcomputer is normal.
Also, JP-A-2002-354871 discloses one instance of a motor-powered steering system in which the second microcomputer computes the magnitude of a motor's d-axis current, and whether the first microcomputer operates normally is determined depending on whether the computed magnitude is larger than a predetermined value.